September 28th, 1889 – The Measure of a Meter

The General Conference on Weights and Measures (French: Conférence générale des poids et mesures – CGPM) is the senior of the three Inter-governmental organizations established in 1875 under the terms of the Metre Convention (French: Convention du Mètre) to represent the interests of member states. The treaty, which also set up two further bodies, the International Committee for Weights and Measures (French: Comité international des poids et mesures– CIPM) and the International Bureau of Weights and Measures (French: Bureau international des poids et mesures – BIPM), was drawn up to coordinate international metrology and to coordinate the development of the metric system.

The conference meets in Sèvres (south-west of Paris) every four to six years. Initially it was only concerned with the kilogram and the meter, but in 1921 the scope of the treaty was extended to accommodate all physical measurements and hence all aspects of the metric system. In 1960 the 11th CGPM approved the Système International d’Unités, usually known as “SI”.

The first ever General Conference on Weights and Measures met on September 28th, 1889 at which point the length of a meter was defined as the distance between two lines on a standard bar of an alloy of platinum with ten percent iridium, measured at the melting point of ice.